Sample surface inspection apparatus and method

ABSTRACT

The present invention provides a surface inspection method and apparatus for inspecting a surface of a sample, in which a resistive film is coated on the surface, and a beam is irradiated to the surface having the resistive film coated thereon, to thereby conduct inspection of the surface of the sample. In the surface inspection method of the present invention, a resistive film having an arbitrarily determined thickness t 1  is first coated on a surface of a sample. Thereafter, a part of the resistive film having the arbitrarily determined thickness t 1  is dissolved in a solvent, to thereby reduce the thickness of the resistive film to a desired level. This enables precise control of a value of resistance of the resistive film and suppresses distortion of an image to be detected.

This application is a divisional of U.S. patent application Ser No.12/153,397, filed May 19, 2008, which is a divisional of U.S. patentapplication Ser. No. 10/511,396, filed on Mar. 23, 2005, now U.S. Pat.No. 7,391,036, issued Jun. 24, 2008, which is a §371 of InternationalApplication No. PCT/JP03/04910 filed on Apr. 17, 2003, which claims thepriority of Japanese Application Nos. 114756/2002 and 129515/2002, filedon Apr. 17, 2002 and May 1, 2002, respectively, all of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a surface inspection apparatus andmethod for effectively performing evaluations, observations, analysesand the like such a structure inspection, an observation in an enlargedview, a material evaluation, an electric conduction and so forth of asample surface. More particularly, the present invention relates to asurface inspection apparatus and method which can detect defects on highdensity patterns having, for example, a minimum line width of 0.15 μm orless on a sample surface, with high accuracy, high reliability and highthroughput. The present invention also relates to a semiconductor devicemanufacturing system which incorporates such a surface inspectionapparatus, and a semiconductor device manufacturing method which employssuch a surface inspection apparatus to inspect patterns in the midway ofa semiconductor device manufacturing process and/or after completion ofthe process.

BACKGROUND ART

Conventionally, when a surface of a sample, such as a substrate or awafer, is observed or subjected to material inspection, or is inspectedor evaluated with respect to a structure or electric continuity ofelectric circuits formed thereon, it is known to use a surfaceinspection apparatus in which a defect in a surface of a sample isdetected by emitting a charged particle beam (a primary charged particlebeam), such as an electron beam, to the surface for scanning, detectingsecondary charged particles emitted from the surface, producing imagedata from the detected secondary charged particles, and comparing theproduced image data with the image data for each die (or chip). Suchsurface inspection apparatuses including one that utilizes a scanningelectron microscope (SEM), and surface flattening apparatuses forflattening a surface of a sample, such as a substrate, exist asindependent apparatuses and have been conventionally used.

In such a conventional SEM-based system as described above, and a systemwhich simultaneously illuminates a wide area on a wafer, as a waferunder inspection is irradiated with an electron beam, the wafer ischarged. The overcharged wafer Would cause distorted image data andobscure images. In addition, a normal pattern may be erroneouslyevaluated as defective.

Another grave problem in the prior art is damages to a sample.Specifically, when an electron beam is irradiated to a surface of awafer, the surface is charged by the irradiated beam, permittingacquisition of an image representative of a potential contrast. However,the wafer may be charged in a different condition depending oninsulating material, metal conductive materials, circuit resistance, andthe like. Therefore, occasionally, an extreme potential difference maybe produced on a boundary of patterns, resulting in failed acquisitionof secondary electrons emitted from the wafer surface or in arcdischarge.

The above-mentioned problems will be described in greater detail.

Secondary electron emission characteristics differ from one sample toanother depending on the energy of an incident irradiated beam thereonand the characteristic of the sample surface. FIG. 1 is a graph showingan exemplary relationship between beam energy and secondary electronemission efficiency η when an insulating material is irradiated with anelectron beam. With η larger than one, more electrons than incidentelectrons are emitted from the insulating material, and hence thesurface of the insulating material is positively charged (Region P). Onthe other hand, with η smaller than one, the surface is negativelycharged (Region Q). This may cause damages such as breakdown in somesamples, the characteristics of which depend on the circuitconfiguration and layered structure thereon.

Specifically, when an insulating material is applied with an electricfield equal to or larger than a breakdown strength (for example, 50-1000kV/mn), the insulating material loses the insulating property to cause abreakdown, resulting in a current flowing therethrough. On the otherhand, when an excessive amount of charge is accumulated on theinsulating material, the field strength exceeds a breakdown voltage,thereby resulting in a breakdown. Also, once a breakdown occurs, anexcessive current flows to break the circuit, and the insulatingmaterial may no longer restore its insulating property.

Further, when the magnitude of a beam current is decreased so as tominimize distortion of the image data due to the electric charge, an S/Nratio of a signal resulting from a secondary charged particle beam,which is emitted from the surface of the sample by emission of a primarycharged particle beam, becomes undesirably low. This increases thepossibility of false detection. The problem of lowering of the S/N ratiomay be lessened and the possibility of false detection may be reduced,by effecting scanning at a plurality of times and conducting anaveraging operation. However, the throughput in such an inspectionapparatus becomes low.

Further, in order to detect fine defects, a large-current emission beamis required. For example, when it is assumed that the amount of signalrequired for determining a defect having a 2×2 pixel size of a CCD is 1,the amount of signal required for determining a defect having a 1×1pixel size is 4. That is, for detecting a fine defect by using the samedetector, the magnitude of a beam current must be increased so as toincrease the amount of secondary electrons. However, when the magnitudeof a beam current is increased, as is described above, the electriccharge on the sample becomes high, thus increasing distortion of theimage.

In order to solve the above-mentioned problems, the Applicant proposed,in Japanese Patent Application No. 2000-340651 (published as JapanesePatent Public Disclosure (Kokai) No. 2002-148227), a method in which aresistive film is coated on the surface of a sample before emission of acharged particle beam to the surface. In this method, however, it isdifficult to form a thin resistive film having a uniform thickness oneach sample. Further improvements are required to be made.

Although a technique of coating a resistive film or coat on the surfaceof the sample before inspection was proposed by the forgoingapplication, no proposals have been made with respect to an inspectionapparatus which enables a series of operations such as surfaceflattening, resistive film coating and emission of a charged particlebeam for inspection to be efficiently conducted. Conventionalindependent apparatuses, such as a flattening apparatus for flattening asurface of a sample, a cleaning apparatus for cleaning a sample, and adrying apparatus, are individually placed with a resistive film coatingapparatus, and each operation is conducted by using these apparatuses.With this arrangement, however, it is difficult to efficiently conductthe above-mentioned series of operations. The reason for this is asfollows. That is, each of the above independent apparatuses comprises asample loading station and a loading/unloading robot. A sample conveyedby a conveyor apparatus for conveying a sample between the apparatusesis temporarily loaded on the sample loading station. Theloading/unloading robot moves the sample from the sample loading stationto a work position, i.e., a stage device, and removes the sample fromthe stage device. A plurality of such independent apparatuses areindividually placed and a conveyor apparatus for conveying a samplebetween the independent apparatuses is further provided. This results ina complicated structure and an increase in overall size of a surfaceinspection apparatus. Further, the time required for conveying thesample is long and the throughput in the entire apparatus is low.Further, the possibility of contamination and oxidation of a surface ofa sample increases, leading to deterioration of product quality.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the problems in the priorarts as mentioned above, and it is an object of the invention to providea sample surface inspection apparatus and method, which is capable ofreliably performing inspections such as observation, detection ofdefects, analysis, and the like on a surface of a sample withoutdamaging the sample.

It is another object of the invention to provide a method for forming aresistive film on a sample and a resistive film forming apparatusenabling an amount of electric charge on a sample to be appropriatelycontrolled and enabling clear image data having minimum distortion to beobtained with respect to a surface of the sample, by making thethickness of the resistive film thin.

It is another object of the invention to provide a surface inspectionmethod and a surface inspection apparatus, wherein even when scanning isconducted using a high-current beam so as to increase a throughput, anamount of electric charge on a sample can be appropriately controlledand clear image data having minimum distortion can be obtained withrespect to a surface of the sample, thus enabling a defect to bedetected by scanning with high reliability.

It is another object of the invention to provide a method and anapparatus for inspecting a surface of a sample with high reliability,wherein the thickness of a resistive film formed on the surface of thesample can be precisely controlled so that a resistive film having adesired thickness can be formed uniformly with respect to each sample,to thereby enable clear image data having minimum distortion to beobtained with respect to the surface of the sample.

It is a further object of the invention to provide a surface inspectionsystem having a simple structure enabled by improving mechanisms forflattening, cleaning and drying a sample, a mechanism for coating aresistive film on a surface of a sample, and a mechanism for conveying asample between the above mechanisms, while maintaining a highthroughput.

It is another object of the invention to provide a surface inspectionsystem which enables a loading/unloading robot of each independentapparatus to be eliminated, thus simplifying the apparatus and a processfor conveyance of a sample, and which is capable of maintaining a highthroughput.

It is another object of the invention to provide a semiconductor devicemanufacturing method which employs the surface inspection apparatus toinspect a semiconductor wafer in the middle of or after completion of aprocess.

In order to achieve the objects, the present invention provides a methodof forming a resistive film on a surface of a sample, which comprisesthe steps of:

rotating the sample at a rotational speed with the sample being held ina substantial horizontal situation;

dropping a liquid film material on the sample surface while the sampleis being rotated, to form a resistive film thereon; and

dropping a solvent which solves the resistive film formed on the samplesurface while the sample is being rotated at a rotational speed, therebydissolving a part of the resistive film to obtain the resistive filmhaving a desired level of thickness.

In the above method, it is preferable that the desired level of thethickness of the resistive film is 0.1 nm to 10 nm, and the resistivefilm is water-soluble.

The present invention further provides an apparatus for forming aresistive film on a surface of a sample, which comprises:

a spin coater which drops a liquid film material on the sample surfacewhile the sample is rotated at a rotational speed with the sample beingheld in a substantial horizontal situation, thereby forming a resistivefilm on the sample surface; and

a film thickness uniformalizing mechanism which makes the thickness ofthe resistive film formed on the sample surface thin and uniform bydissolving a part of the resistive film with a solvent.

In the above apparatus, it is preferable that the film thicknessuniformalizing mechanism includes a solvent dropping device which dropsa solvent dissolving the resistive film while the sample is rotated.

The present invention further provides a method of inspecting a surfaceof a sample, which comprises the steps of;

coating the sample surface with a resistive film having an arbitrarilydetermined thickness;

dissolving a part of the resistive film, to thereby reduce the thicknessof the resistive film to a desired level which is thinner than that ofthe arbitrarily determined thickness; and

irradiating a charged particle beam to the sample surface coated withthe resistive film, to thereby conduct inspection of the sample surface.

In the above method, it is preferable that the desired level of thethickness of the resistive film is 0.1 nm to 10 nm, the resistive filmis water-soluble, and the method further comprises the step of removingthe resistive film from the sample surface by cleaning it with purewater or ultrapure water after the inspection of the sample surface.

The present invention further provides a system for inspecting a surfaceof a sample, which comprises:

a surface flattening mechanism for flattening the sample surface;

a resistive film coating mechanism for coating a resistive film on thesample surface after the surface is flattened by the surface flatteningmechanism, the resistive film having an arbitrarily determinedthickness, and then dissolving a part of the resistive film in asolvent, to thereby reduce the thickness of the resistive film to adesired level;

an inspection mechanism for emitting a charged particle beam to thesample surface having the resistive film coated thereon, to therebyconduct inspection of the sample surface; and

a conveyor mechanism for conveying the sample between the mechanisms.

In the above system, it is preferable that the system further comprisesa cleaning mechanism and a sample drying mechanism so that the sample ina clean and dry state is introduced into and removed from the surfaceinspection apparatus, wherein the surface flattening mechanism, theresistive film coating mechanism, the inspection mechanism, the cleaningmechanism and the sample drying mechanism are disposed so as to surroundthe conveyor mechanism.

The present invention further provides a mechanism for inspecting asurface of a sample, comprising:

an electromagnetic wave irradiation apparatus comprising anelectromagnetic wave source, and a device for guiding an electromagneticwave generated from the electromagnetic wave source onto a samplesurface;

a detector for detecting electrons emitted from the sample surface whichis irradiated with the electromagnetic wave to output an electric oroptical signal; and

a processing unit for processing the electric or optical signal from thedetector for evaluation of the sample surface.

In the above mechanism, it is preferable that the electromagnetic wavesource is a source which emits an ultraviolet or X-ray laser, or anultraviolet ray or X-ray having a wavelength of 400 nm or less. Themechanism could further comprises: an electron beam irradiationapparatus comprising an electron beam source, and a device for guidingan electron beam generated from the electron beam source onto the samplesurface; and an apparatus for driving one or both of the electromagneticwave irradiation apparatus and the electron beam irradiation apparatusto irradiate the sample surface with one or both of the electromagneticwave or the electron beam. The mechanism could further comprises animaging optical system for guiding the electrons emitted from the samplesurface to the detector.

The present invention further provides a method of manufacturing asemiconductor device comprising the step of inspecting a semiconductorwafer in the middle of a manufacturing process and/or after completionof the manufacturing process, using the inspection apparatus or systemas above or by the inspection method as above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship between beam energy andsecondary electron emission efficiency;

FIG. 2 is a cross-sectional view of a silicon wafer on which a resistivefilm is coated;

FIG. 3 is a graph indicating the relationship between the speed ofrotation (rpm) of a wafer and the thickness of a resistive film formedon the wafer by a spin coater;

FIGS. 4(A)-4(C) are cross-sectional views for explaining a method foruniformalizing a thickness of a resistive film according to theinvention;

FIG. 5 is a graph indicating the relationship between the thickness ofthe resistive film remaining on the wafer and the supply amount ofultrapure water when the resistive film coated on the wafer is dissolvedin ultrapure water;

FIG. 6 is an exaggerated cross-sectional view showing an example inwhich a stepped pattern is formed on a silicon wafer;

FIG. 7 is a graph indicating the relationship between the thickness ofthe resistive film remaining on the wafer and the supply amount ofultrapure water, when the resistive film coated on the wafer isdissolved in ultrapure water under a condition different to that of thecase shown in FIG. 5;

FIGS. 8(A) and 8(B) are exaggerated cross-sectional views showing anexample in which a stepped pattern is formed on a silicon wafer;

FIG. 9 is a schematic plan view showing disposition of mechanismsforming a surface inspection system for carrying out a surfaceinspection method according to the invention;

FIG. 10 is a schematic explanatory view of a conveyor robot of aconveyor mechanism applicable to the surface inspection system as shownin FIG. 9;

FIG. 11 is a schematic side view for explaining an example of a filmthickness uniformalizing mechanism applicable to the system as shown inFIG. 9;

FIGS. 12(A)-12(C) are schematic side views for explaining other examplesof film thickness uniformalizing mechanisms applicable to the systemshown in FIG. 9;

FIG. 13 is a schematic perspective view for explaining a further exampleof a film thickness uniformalizing mechanism applicable to the systemshown in FIG. 9;

FIG. 14 is a diagram showing a general construction of a firstembodiment of a surface inspection apparatus (or mechanism) applicableto the system shown in FIG. 9;

FIG. 15 is a diagram showing a general construction of a secondembodiment of a surface inspection apparatus (or mechanism) applicableto the system shown in FIG. 9;

FIG. 16 is a diagram showing a general construction of a thirdembodiment of a surface inspection apparatus (or mechanism) applicableto the system shown in FIG. 9;

FIG. 17 is a diagram showing a general construction of a fourthembodiment of a surface inspection apparatus applicable (or mechanism)to the system shown in FIG. 9;

FIG. 18 is a diagram showing a general construction of a fifthembodiment of a surface inspection apparatus (or mechanism) applicableto the system shown in FIG. 9;

FIG. 19 is a diagram showing a general construction of a sixthembodiment of a surface inspection apparatus (or mechanism) applicableto the system shown in FIG. 9;

FIG. 20 is a diagram showing a general construction of a seventhembodiment of a surface inspection apparatus (or mechanism) applicableto the system shown in FIG. 9;

FIG. 21 is a flowchart illustrating a semiconductor device manufacturingmethod according to the invention; and

FIG. 22 is a flowchart illustrating a lithography process illustrated inFIG. 21 in greater detail.

BEST MODE FOR CARRYING THE INVENTION

Referring to the drawings, description is made with regard toembodiments of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a sample S to beinspected by a surface inspection method of the present invention. Inthis embodiment, as the sample S, a silicon wafer (hereinafter, referredto simply as “a wafer”) W during a semiconductor device manufacturingprocess, on which an arbitrarily determined pattern p such as anelectronic circuit has been formed, is taken as an example. In aninspection process or some processes for manufacturing semiconductorcircuit, an electron beam is emitted to a surface of the wafer W [in thefollowing explanation of this embodiment, an electron beam (a primaryelectron beam) is taken as an example of a charged particle beam emittedto a wafer], and the resulting electron beam (a secondary electron beam)emitted from the wafer W is detected, to thereby conduct inspection ofthe surface of the wafer W. Such inspection is conducted to detectforeign matter, a defect in electric continuity, a defect or loss of apattern, determine a wafer condition or determine the types of wafersfor sorting. However, when the magnitude of a current of an electronbeam emitted to the wafer W is increased, the electric charge on thewafer W increases, thus generating distortion of image data producedfrom detected secondary electrons, and preventing accurate detection.

In order to solve this problem, in the above-mentioned patentapplication, the Applicant proposed a method of controlling the amountof electric charge on the wafer by coating a resistive film f on thewafer. However, it was found that the amount of electric charge on thewafer cannot be precisely controlled simply by coating a resistive filmon the wafer. That is, when a resistive film is formed by using aso-called spin coater, as is indicated in FIG. 3, the thickness ofresistive film becomes small as the speed of rotation (revolutions perminute) of the wafer increases, but the thickness of resistive film doesnot decrease when the rotation speed of the wafer exceeds a certainlevel, namely, about 2,000 rpm. In fact, it is impossible to obtain aresistive film having a thickness less than about 20 nm.

As is explained with reference to FIG. 1, with a high beam energy suchthat η larger than 1, the number of electrons emitted from theinsulating material is larger than that of incident electrons.Therefore, the surface of the insulating material is positively charged.The value of resistance and the thickness of a resistive film are hereinimportant. When the value of resistance is as small as that of ametallic film, a potential contrast of the image becomes low, anddistortion of the image is suppressed. However, pattern recognitionbecomes poor and detection of a defect becomes difficult. When the valueof resistance is too large, the image is distorted to a large extent.Secondary electrons emitted from a part of the surface cannot beobtained, and arc discharge occurs.

In the present invention, as in conventional techniques, the surface ofthe wafer W (in this embodiment in which the pattern p is formed on anupper surface of the wafer W, the surface of the layer of pattern p) isflattened, by means of a surface flattening mechanism, such as a CMP(Chemical Mechanical Polishing) apparatus having a structure known inthe art or a reactive ion flattening apparatus using plasma (FIG. 4(A)).Subsequently, as shown in FIG. 4(B), a resistive film material m inliquid form is sprayed over the flattened surface of the wafer W whilethe wafer W is rotated, by a conventional spin coater, to thereby form aresistive film f. Coating is conducted so that the thickness of theresistive film f becomes a thickness t₁ which is larger than a desiredthickness to be finally obtained. As a resistive film material, use ismade of, for example, a metal-containing polymer material or a polymercompound of a thienyl alkane sulphonate type. The value of resistance isabout 1×10⁶ to 100×10⁶Ω (per cm², for example; a film thickness: 0.1 nmto 100 nm). A resistive film made of a polymer compound of a thienylalkane sulphonate type is water-soluble, which is advantageous in afilm-removing process described later. Instead of a polymer compound ofa thienyl alkane sulphonate, similar coating materials of an acrylictype or a chemical amplification type may be used. According to thepresent invention, by appropriately selecting the value of resistance,image distortion can be minimized and surface inspection can beconducted efficiently while reducing the risk of false detection. Wheninspection is conducted during an LSI manufacturing process,removability of the resistive film is important because after theinspection, the resistive film must be removed before subjecting thewafer to the subsequent process. Therefore, use of a water-solubleresistive film is of great importance in the present invention.

As is described above, the thickness of a resistive film which can beobtained by a spin coater is limited. In fact, it is impossible to forma resistive film having a thickness less than 20 nm. Therefore,conventionally, a wafer coated with a resistive film having a thicknessof 20 nm or more is subjected to inspection.

This is problematic, however, in the following point. That is, whenacquiring secondary electrons emitted from the wafer by emission of aprimary electron beam, an error in acquisition due to the thickness ofthe resistive film occurs. For example, when electrons pass through theresistive film, due to lowering of a electric field for extraction,secondary electrons are dispersed, leading to a low contrast and a blurof the image.

To prevent these problems, it is desired to further reduce the thicknessof the resistive film. However, as is described above, conventionalcoating methods are unsatisfactory.

Therefore, in the present invention, as shown in FIG. 4C, a solvent(pure water or ultrapure water n in this embodiment) for the resistivefilm f is uniformly sprayed over an upper surface of the resistive filmf having the thickness t₁ formed by the spin coater, to thereby dissolvean upper-side portion of the resistive film f so that the remainingresistive film has a uniform thickness t₂. After the film thickness t₂is obtained, by using an inspection mechanism described later and amethod known in the art, a primary electron beam, which is a type of acharged particle beam, is emitted to the surface of the wafer W as thesample S, on which the pattern p is formed. A secondary electron beam isemitted from the wafer W and acquired for inspection and evaluation.

Experiments were conducted, in which a resistive film was formed on awafer by a spin coater (the thickness of the resistive film at this timewas 20 nm), and then ultrapure water is sprayed to thereby dissolve theresistive film. As a result, the relationship between the thickness ofthe resistive film remaining on the wafer and the supply amount ofultrapure water, such as that shown in FIG. 5, was obtained. From FIG.5, it is apparent that a final thickness of the resistive film can becontrolled by appropriately controlling the supply amount of a solventfor dissolving the resistive film, such as pure water or ultrapurewater.

FIG. 6 shows a sample S′ on which steps are formed on a surface of alayer of pattern p (which steps are formed by a plurality of lines l).In this embodiment also, coating of a resistive film and control of afilm thickness can be conducted by the same method as explained above inconnection with FIG. 3. In this embodiment, the lines l are spacedequidistant from each other. In the case where distances between thelines l are substantially different, surface electrification becomesdifferent, depending on the distance between the lines l. However, amethod of the present invention of forming a thin resistive film havinga uniform thickness is effective in obtaining a uniform surfacepotential.

The water solubility varies according to a type of a resistive film tobe applied, a molecular structure thereof, a type of an addition agent,a concentration of a solution and the like. FIG. 7 is a graphrepresenting a relationship between a thickness of a film and a supplyamount of pure water, observed under a condition different to thatemployed in FIG. 5.

In an embodiment of a resistive film forming process, a resistive filmsolution of a polymer compound of a thienyl alkane sulphonate orisothianaphthenediyl-sulphonate can be employed to form a resistivefilm. The relationship shown in FIG. 7 represents a film thicknessfeature in a case that a polymer compound ofisothianaphthenediyl-sulphonate and surfactant is utilized as aresistive film solution, the a sample is placed in a spin coater and aresistive film solution is dropped on the sample. Next, the sample iscoated with a resistive film, on the spin coater at a rotational speedof, for example, 5000-7000 rpm. Thereby, a resistive film having athickness of approx. 20 nm is formed. In dissolving the thus formedresistive film, the sample is placed in the spin coater and pure wateris dropped on the sample while rotating the spin coater. A rotationalspeed of the coater is 5000-10,000 rpm. The resistive film is dissolvedwith pure water or ultrapure water. FIG. 7 shows a thickness of theresistive film remaining on the sample after dissolution. As is clearfrom the graph, a thickness of a resistive film can be controlled byadjusting the amount of pure water or ultrapure water to be supplied todissolve the resistive film.

In conducting an inspection to detect wafer defects, at first aresistive film is formed on the wafer by a process similarly to theabove-described embodiment of a resistive film forming process. Forexample, a Si wafer on which an LSI device structure has been formed isprepared and a resistive film of a polymer compound ofisothianaphthenediyle-sulphonate is deposited to be 1 nm in thickness onthe Si wafer. Since a thickness of the resistive film formed on thewafer is controllable by the above-mentioned process, a clear electronimage with suppressed charge-up, small distortion and minor contrastdeterioration can be obtained. Since a contrast of an electron imagevaries according to a material and structure of a surface, an evenclearer electron image having minimum distortion can be obtained bycontrolling for a resistive film to have an appropriate thickness.

Further, a resistive film forming process can be executed on a photomask and/or reticle mask.

FIGS. 8(A) and 8(B) illustrate cross-sectional views of a photo mask andthe same with a resistive film coated thereon. A material of a basestructure of the photo mask is silicon glass or quartz glass having athickness of 1 mm and a material of a pattern is Cr, as shown in FIG.8(A). A size of the mask is 8×8 inches, a size of a portion of a patternbeing 20×20 mm and a size of a minimum pattern being approximately0.5-0.3 μm. The Cr pattern formed on the substrate has a thickness of0.1 μm. A resistive film is applied to the surface of the mask by meansof spin coating to have a film thickness of 20 nm. Subsequently, thefilm is dissolved with ultra pure water to have a thickness of 5 nm.

Next, an inspection to detect defects such as pattern defects on thephoto mask with the resistive film is conducted by using a scanningelectron microscope. Instead of using a scanning electron microscope, anmapping projection method may be employed to conduct an inspection todetect a defect by an electron beam.

If any defect is not found in the inspection, the resistive film isremoved by cleaning with ultrapure water in a cleaning mechanism. Afterthe resistive film is removed, the mask can be used as a proper photomask again for an exposure system.

Although the above example employs a photo mask, the same processing asset forth above may be performed on a reticle mask. In the case of areticle mask, a pattern reduction rate would be ½-⅕ and a transferredminimum line width would be approximately 0.1-0.5 μm.

In a photo mask or reticle mask, a thin film pattern of metal such as Crand the like is generally deposited on a surface of a glass material.Since a base material is an insulation glass material such as siliconglass, quartz glass and the like, the surface is allowed to charge-upheavily when an electron beam is applied, which makes it difficult toconduct inspection using an electron beam.

In the present invention, a photo mask or reticle mask is coated with aresistive film to thereby stabilize the potential on the surface of themask. Thus, even though an electron beam is applied to the mask,charge-up of the mask is obviated and inspection by means of irradiationof an electron beam becomes possible. This is applicable to a scanningelectron microscope, projection electron microscope, an inspectionapparatus employing an electron beam and the like.

In the resistive film forming method according to the present invention,the thickness of a resistive film on a sample can be preciselycontrolled so that a resistive film having a desired thickness can beformed uniformly with respect to each sample. Therefore, it is possibleto precisely control the amount of electric charge generated by emissionof a beam, such as an electron beam or an ion beam, so that a clearpotential-contrast image having minimum distortion can be obtained.Conventionally, the thickness of a resistive film cannot be reduced to alevel lower than 20 nm. However, a resistive film having a thickness of0.1 to 1 nm can be obtained in the present invention. Thus, the electriccharge on a sample substrate can be appropriately controlled, so that anelectron image which is most satisfactory in terms of a potentialcontrast and distortion can be obtained.

When an electron beam or an ion beam is emitted to a sample substrate,in the case where the beam has an energy as high as about 2 keV or more,there is a possibility of the substrate or device circuits formedthereon being damaged. This possibility can be reduced by effectingobservation or inspection according to the present invention. With ahigh beam energy that will cause device damage in conventionaltechniques, such damage does not occur and an electron image havingminimum distortion can be obtained in the present invention.

In the above resistive film forming process, the desired level of thethickness of the resistive film may be 0.1 nm to 10 nm. The resistivefilm may be water-soluble. In this case, after inspection of the samplesurface, the resistive film may be removed by cleaning with pure wateror ultrapure water.

FIG. 9 is a general plan view of an embodiment of a surface inspectionsystem for carrying out a surface inspection method of the presentinvention. A surface inspection system 100 in this embodiment comprisesa central conveyor mechanism 200, and a flattening mechanism 300, acleaning mechanism 400, a drying mechanism 500, a resistive film coatingmechanism 600, an inspection mechanism 700 and a wafer stock interface800 surrounding the conveyor mechanism 200.

As shown in FIG. 10, the conveyor mechanism 200 comprises a movabletable 210 movable horizontally (in a lateral direction in FIG. 10) and aplurality of (two in this embodiment) articulated conveyor robots 220 aand 220 b attached to the movable table 210. The conveyor robots 220 aand 220 b may have the same structure which is known in the art. Eachconveyor robot comprises a base 230, an articulated arm 250 and a chuck260. The base 230 is vertically movable relative to the movable table210 and pivotable about an axis 240-240. The articulated arm 250 isconnected to the base 230. The chuck 260 is connected to a forward endarm of the articulated arm 250 so as to hold a wafer W. The articulatedarm 250 may have a known structure which comprises a plurality of (threein this embodiment) arm members connected so as to be pivotally movablerelative to each other. The chuck 260 also may have a known structure.Therefore, detailed description of structures and operations of thearticulated arm 250 and the chuck 260 is omitted. The conveyor mechanism200 conveys a wafer between the above mechanisms 300, 400, 500, 600 and700, and between each mechanism and the wafer stock interface 800. Awafer held by the chuck 260 of the conveyor robot 220 a or 220 b isdirectly loaded on a work station of each mechanism, that is, a stagedevice, and a wafer is unloaded from the stage device directly by theconveyor robot 220 a or 220 b. Therefore, differing from conventionalindependent apparatuses which conduct the same operations as theabove-mentioned mechanisms, a loading/unloading robot for each mechanismcan be eliminated. Further, in the conveyor mechanism 200 in thisembodiment in which a plurality of conveyor robots 220 a and 220 b areprovided, when a wafer is loaded on or unloaded from, for example, thecoating mechanism 600, a new wafer held by one conveyor robot 220 a ismoved to a position close to the coating mechanism 600, and a waferafter coating is removed from the coating mechanism 600 by the otherconveyor robot 220 b, and the new wafer held by the conveyor robot 220 ais placed on a stage device of the coating mechanism 600. Thus, a waferis loaded on or unloaded from a stage device of each mechanism directlyby the conveyor mechanism 200. Therefore, the loading/unloading robotsfor the respective mechanisms can be eliminated, thus eliminatingoperations of these robots and simplifying a conveying process.

A basic arrangement of the flattening mechanism 300 may be the same asthose of a CMP apparatus having a known structure, a reactive ionflattening apparatus using plasma, etc. Therefore, detailed descriptionof a structure and an operation of the flattening mechanism 300 isomitted. The flattening mechanism 300 differs from a conventionalindependent flattening apparatus such as a conventional CMP apparatus inthat a wafer is loaded on a work station, namely, a stage device 310,directly by means of the conveyor robot 220 a or 220 b of the conveyormechanism 200, and that a wafer loading station and a loading/unloadingrobot for conveying a wafer between the conveyor mechanism 200 and thestage device 310 are not provided.

A basic arrangement of the cleaning mechanism 400 may be the same asthat of a conventional cleaning apparatus adapted to clean a wafer usingpure water or ultrapure water, except that a loading/unloading robot anda wafer loading station are eliminated. Therefore, detailed descriptionof a structure and an operation of the cleaning mechanism 400 isomitted. A wafer is loaded on a stage device 410 directly by theconveyor mechanism 200. The drying mechanism 500 may be a conventionaldrying apparatus of a type which blows dry air or a nitrogen gas againsta wafer, a vacuum drying type or a heat-drying type. Therefore, detaileddescription of a structure and an operation of the drying mechanism 500is omitted. The drying mechanism 500 differs from a conventionalindependent drying apparatus in that a wafer is loaded on a stage device510 directly by the conveyor robot 220 a or 220 b of the conveyormechanism 200, and that a wafer loading station and a loading/unloadingrobot for conveying a wafer between the conveyor mechanism 200 and thestage device 510 is not provided.

The resistive film coating mechanism 600 comprises a conventionalcoating apparatus, such as a spin coater, and a film thicknessuniformalizing mechanism 650 for dissolving a part of a resistive filmto thereby reduce and uniformalize the thickness of the resistive film.Therefore, in the resistive film coating mechanism 600, a mechanism forcoating a resistive film is the same as that of a conventional spincoater and is therefore not described in detail. Only a basicarrangement of the film thickness uniformalizing mechanism 650 isexplained, with reference to FIG. 11.

Referring to FIG. 11, the film thickness uniformalizing mechanism 650comprises a micro syringe 660 movable to a position above a rotor 610 ofthe resistive film coating mechanism 600. The micro syringe 660 isconnected through a control valve 680 and a flexible pipe to a supplysource 670 of pure water or ultrapure water. In the film thicknessuniformalizing mechanism 650, a wafer W is held on the rotor 610 of aspin coater under force of vacuum, and a resistive film material inliquid form is sprayed from a film material dropping head 620 over thewafer W, to thereby conduct coating. At this time, a resistive filmhaving a thickness t₁ is formed on the wafer W. Thereafter, the filmmaterial dropping head 620 is moved away from the position above therotor 610, and the micro syringe 660 is moved to that position, in placeof the film material dropping head 620. Then, while the wafer W isrotated at a rate of, for example, 3,000 rpm to 7,000 rpm by the rotor61, pure water or ultrapure water n from the supply source 670 isjet-sprayed or shower-sprayed through a spray opening 6610 of the microsyringe 660 uniformly over an upper surface of the resistive film fcoated on the wafer W. Because the resistive film f is water-soluble, anupper-side portion of the resistive film which makes contact with purewater or ultrapure water is dissolved. The thickness t₂ of the resistivefilm to be left on the wafer W is controlled by determining the supplyamount of pure water or ultrapure water in consideration of the surfacearea of the wafer W and the initial film thickness t₁. The thickness t₁of the resistive film at the time of completion of coating by a spincoater can be made 20 nm, which is a lower limit of a film thicknessobtained by using a conventional spin coater. However, the thickness t₁may be larger than 20 nm. The thickness t₂ of the resistive film fremaining on the wafer W after dissolution of a part of the resistivefilm f in a solvent, such as pure water or ultrapure water, ispreferably 0.1 nm to 10 nm. When the film thickness t₂ is smaller than0.1 nm, an effect of suppressing charge-up cannot be obtained, thuspreventing high-precision observation. When the thickness t₂ is largerthan 10 nm, the number of detected electrons (such as secondaryelectrons) emitted from the resistive film f itself increases, andelectrons (such as secondary electrons) emitted from the surface of asample (such as a wafer) underneath the resistive film are scatteredwithin the resistive film, thus generating a change in an electron orbitand deterioration of an acquisition value (a blur). The thickness t₂ ofthe resistive film f is more preferably 0.5 nm to 2 nm.

FIG. 12(A) shows another example of a film thickness uniformalizingmechanism. In this example, while a wafer W is placed on the rotor 610and rotated (at a rate of, for example, 1,000 to 10,000 rpm), a supplyhead 660 a is disposed at a position above the wafer W (at a height hfrom the wafer W). The supply head 66 a extends along a diameter passingthrough the axis of rotation of the rotor 610. The supply head 66 aincludes a number of flow apertures 6610 a formed in a lower surfacethereof, which are arranged at predetermined spaced intervals in alongitudinal direction of the supply head 660 a. Pure water or ultrapurewater flows from the flow apertures 6610 a, to thereby dissolve a partof the resistive film f in pure water or ultrapure water. In this case,the thickness t₂ can be controlled by controlling a total amount of purewater or ultrapure water supplied from the supply head 66 a through theflow apertures 661 a, by means of the control valve 680. Instead of thesupply head 66 a having the flow apertures 6610 a, a supply head 660 bas shown in FIG. 12(B) may be used. The supply head 660 b includes aplurality of (five in this example) nozzles 6610 b formed on a lowersurface thereof, each having a cross-section such as that shown in FIG.12(C). In this case, pure water or ultrapure water is jet-sprayed fromthe nozzles 661 b. In either case, the distance h between the flowapertures 6610 a or the nozzles 6610 b and the surface of the resistivefilm f on the wafer W should be appropriately selected so that purewater or ultrapure water can be sprayed uniformly all over the uppersurface of the resistive film f. FIG. 12(D) shows a further example of afilm thickness uniformalizing mechanism. In this example, while a waferW is rotated by the rotor 610, a supply head 660 c is moved reciprocallyor in one direction between an axis O-O of rotation of the rotor 610 anda position at an outer periphery of the rotor 610, along a diameterpassing through the axis O-O of rotation of the rotor 610. Thus, purewater or ultrapure water is sprayed from nozzles 6610 c of the supplyhead 660 c, to thereby dissolve the resistive film f.

FIG. 13 shows a still further example of a film thickness uniformalizingmechanism. In this example, a supply head 660 d is disposed above therotor 610. The supply head 660 d includes a plurality of nozzles 6210 dfor spraying a film material in liquid form over a wafer and a pluralityof nozzles 6610 d for spraying a solvent such as pure water or ultrapurewater over a resistive film. The nozzles 6210 d are connected to asupply source 630 d of a film material in liquid form, and the nozzles6610 d are connected to a supply source 670 d of a solvent. With thisarrangement, it is unnecessary to move the supply head for coating aresistive film or for supplying a solvent.

The thickness t₂ of the resistive film remaining on the wafer afterdissolution of an upper-side portion of the resistive film is measuredby an optical measurement method using an ellipsometer, or a methodusing a step height measurement device, such as a surface roughnessmeasurement device or an atomic force microscope. If desired,measurement of a film thickness can be conducted more precisely by usingAuger spectroscopy, SIMS, or characteristic X-ray analysis measurement.

Measurement of a film thickness may be conducted with respect to eachwafer, although a cumbersome operation is required and a throughputlowers. Normally, suitable conditions are preliminarily determined byconducting experiments so as to obtain the relationship between the filmthickness t₂ (obtained after dissolution of a part of a resistive film)and various conditions, such as the supply amount of pure water orultrapure water, the rotation speed of a wafer and the film thickness t₁prior to dissolution. Uniformalization of the film thickness isconducted based on this relationship, and reproducibility in the filmthickness due to variation in the conditions is examined by sampling.Therefore, the surface inspection system in this embodiment does notinclude a device for measurement of a film thickness.

After uniformalization of the film thickness, the wafer is introducedinto the inspection mechanism (or surface inspection apparatus) 700. Asto the inspection mechanism 700, embodiments thereof will be explainedlater.

The wafer stock interface 800 (in FIG. 9) includes a plurality of (atleast two) cartridges, each accommodating a plurality of wafers arrangedvertically in a spaced relationship. A wafer can be removed from thecartridge by means of the conveyor robot 220 a or 220 b of the conveyormechanism 200. This arrangement is known in the art. Therefore, detaileddescription of the wafer stock interface 800 is omitted.

By providing the components of the surface inspection system 100 (i.e.,the central conveyor mechanism 200, the flattening mechanism 300, thecleaning mechanism 400, the drying mechanism 500, the resistive filmcoating mechanism 600, the inspection mechanism 700 and the wafer stockinterface 800) in one large chamber, and maintaining the inside of thechamber in a vacuum or an inert gas atmosphere, contamination of wafersduring conveyance can be prevented.

Using the surface inspection system 100 as illustrated in FIG. 9, awafer is processed in the following sequence of steps.

-   1) Pre-Processing: a wafer is pre-processed.-   2) Wafer Conveyance: after pre-processing, the wafer is supplied to    a wafer station 810 of the wafer stock interface 800.-   3) Wafer Loading: the wafer is loaded on the conveyor robot 220 a or    220 b of the conveyor mechanism 200.-   4) Wafer Cleaning: the wafer is conveyed to the cleaning mechanism    400 by the conveyor robot 220 a or 220 b, and cleaned.-   5) Flattening: the wafer is conveyed to the flattening mechanism 300    by the conveyor robot 220 a or 220 b, and flattened.-   6) Cleaning: the wafer is conveyed to the cleaning mechanism 400 by    the conveyor robot 220 a or 220 b, and cleaned.-   7) Drying: the wafer is conveyed to the drying mechanism 500 by the    conveyor robot 220 a or 220 b, and dried.-   8) Resistive Film Coating and Film Thickness Control: the wafer is    conveyed to the resistive film coating mechanism 600 by the conveyor    robot 220 a or 220 b, and coated with a resistive film having a    desired thickness t₁.-   9) Inspection: the wafer is conveyed to the inspection mechanism 700    by the conveyor robot 220 a or 220 b, and an electron beam or    electromagnetic wave beam is emitted to the wafer for inspection.-   10) Cleaning: the wafer is conveyed to the cleaning mechanism 400 by    the conveyor robot 220 a or 220 b, and the resistive film on the    wafer is completely removed.-   11) Drying: the wafer after cleaning is conveyed to the drying    mechanism 500 by the conveyor robot 220 a or 220 b, and dried.-   12) Wafer Unloading: the wafer is conveyed to a wafer station 820 of    the wafer stock interface 800 by the conveyor robot 220 a or 220 b.-   13) Wafer Conveyance: the wafer is conveyed to a post-process.-   14) Post-Processing: the wafer is post-processed.

A plurality of wafers can be processed at the same time in the aboveoperating sequence, using the surface inspection system of the presentinvention. For example, while one wafer is being flattened, anotherwafer can be coated with a resistive film and inspected. Thus, it ispossible to reduce the time required for processing wafers for devicemanufacturing. Therefore, processing time for each sample can be reducedand a defect in each process can be early detected.

The surface inspection system illustrated in FIG. 9 may be additionallyprovided with a repairing mechanism, a pattern forming mechanism, adeveloping mechanism, a resin film coating mechanism and the like. Inthis way, it is possible to flatten, form patterns, evaluate patternforming masks for defects, and repair defective masks.

Embodiments of the inspection mechanism 700 will next be explained withreference to FIGS. 14-20. It should be noted that these embodiments canbe employed dependently and independently on the system shown in FIG. 9.

FIG. 14 shows a first embodiment of the inspection mechanism 700, whichis an electron beam apparatus. The electron beam apparatus 700 shown inFIG. 14 is an imaging projection type electron beam apparatus whichcomprises an electron gun 71 for emitting a primary electron beam (ashaped beam) 72 shaped by a square opening, a primary electron opticalsystem (hereinafter, referred to simply as “the primary optical system”)73 for emitting the primary electron beam 72 to a wafer W, a secondaryelectron optical system (hereinafter, referred to simply as “thesecondary optical system”) 75 for acquiring secondary electrons 74emitted from the wafer W by the irradiation of the primary electron beam72, and a detector 76 for detecting the secondary electrons 74. In thiselectron beam apparatus 700, the primary electron beam 72 emitted fromthe electron gun 71 is reduced by two lens systems 731 and 732 of theprimary optical system 73, and an image is formed in a size of 1.25square mm at a center plane of an ExB separator 733. The electron beamdeflected by the ExB separator 733 is reduced to ⅕ by lenses 736 and737, and projected on the wafer W. The secondary electrons 74 havingpattern image data emitted from the wafer W pass through the lenses 736and 737. The secondary electron beam is then magnified by magnificationlenses 751 and 752 of the secondary optical system 75, and forms asecondary electron image at the detector 76. In this electron beamapparatus, the ExB separator 733 is adapted to deflect the primaryelectron beam 72 emitted from the electron gun 71, while allowing thesecondary electrons 74 from the surface of the sample to passstraightforward through the ExB separator 733, and the primary electronbeam 720 to become incident at a right angle on the surface of thesample.

Of the four magnification lenses 736, 737, 751 and 752, the lenses 736and 737 form a symmetrical doublet, and the magnification lenses 751 and752 also form a symmetrical doublet, thus providing a lens system havingno distortion. However, slight distortion will be generated due tocontamination of electrodes. Therefore, periodically, a referencepattern is placed at the sample plane, and measurement of distortion isconducted to calculate a parameter for correction of distortion.

When inspection is conducted by the imaging projection type electronbeam apparatus shown in FIG. 14, with respect to a wafer on which anoxide film or a nitride film is selectively formed, the problem ofdistortion cannot be effectively avoided by only correcting distortionof an optical system. After acquisition of image data, selected pointson a pattern edge are compared with a data image, to thereby correctdistortion. Thereafter, comparison is made between dies (or chips), orbetween image data and a data image, to thereby detect a defect.

In the inspection mechanism 700 comprising an electron beam apparatus inthis embodiment, a conveyor robot for conveying a wafer from theconveyor mechanism 200 to a stage 770 of the electron beam apparatus ofthe inspection mechanism 700 is not provided.

FIG. 15 shows a second embodiment of a sample surface inspectionapparatus or mechanism 700. The inspection apparatus in this examplecomprises a scanning type electron beam apparatus. This scanning typeelectron beam apparatus 700 comprises an electron gun 71 a for emittinga primary electron beam, a primary electron optical system (hereinafter,referred to simply as “the primary optical system”) 73 a forilluminating a wafer W with the primary electron beam which has beenemitted from the electron gun 71 a and shaped, and a detector 76 a fordetecting electrons, such as secondary electrons, emitted from the waferW. In this electron beam apparatus, primary electrons emitted from theelectron gun 71 a are accelerated by anode, and pass through an apertureformed by an aperture plate 731 a of the primary optical system 73 a, tothereby form an electron beam 72 a, which in turn passes through lenssystems 732 a and 733 a and illuminates the wafer W on which theresistive film f is formed. A scanning operation and magnification ofthe primary electron beam 72 a are controlled by a scanning coil 734 aand a lens system 735 a. Secondary electrons, backscattered electrons orreflected electrons emitted as a result of irradiation of the primaryelectron beam 72 a are detected by the detector 76 a, such as aphotomal, and form a secondary electron image. The wafer W is attachedto a movable stage 770, and continuously moved in an X- or Y-directionat a rate corresponding to an image magnification. Thus, a continuousimage can be obtained, by using a liner sensor. Using this secondaryelectron image, comparison is made between dies (or chips) or betweenimage data and a data image, thus detecting a defect in the wafer W.

FIGS. 16-20 respectively show third through seventh embodiments of aninspection mechanism 700. In FIGS. 16-20, the same reference numeralsdenote the same or similar components.

First, the concept of these embodiments of the apparatus will bedescribed below.

Each of these embodiments is characterized in that an electromagneticwave is irradiated onto a surface of a sample, photoelectrons generatedthereby is detected, and an image is formed on the basis of theelectrons. Particularly, electromagnetic waves having wavelengths of 400nm or less such as ultraviolet rays, X-rays and the like, are suitableto utilized in the invention. Such electromagnetic waves can limit theamount of charge on the sample surface, so that less distorted imagescan be obtained. Also, the electromagnetic wave can be uniformlyirradiated even when a potential distribution occurs on the samplesurface. It is therefore possible to acquire a uniform and clearpotential contrast image in the field of view.

Also, since the electromagnetic waves are consistent in irradiationcharacteristic irrespective of the properties of materials irradiatedtherewith, they can be irradiated to any material. For example, theelectromagnetic waves can be similarly irradiated to such samples assemiconductor, LSI, metal, insulating material, glass, living material,polymer material, ceramic, or a composite material thereof, to evaluatethe sample surface.

The surface inspection apparatus comprises an electron beam generatortogether with an electromagnetic wave generator, so that they can beselectively driven for irradiation or simultaneously driven forirradiation. For example, for evaluating a surface of a semiconductorwaver on which a variety of circuit configurations are formed overmultiple layers, an electromagnetic wave can be irradiated to a circuitand a layered structure which must be protected from damages, while anelectron beam can be irradiated to a circuit and a layered structurewhich need not be protected from damages.

When damages need not be taken into consideration, a sample can beirradiated with an electron beam having electron irradiation energyselected approximately in a range of 0 to 4 keV to provide best images.For example, when an electron beam having 2-3 keV is irradiated to awafer having simple L/S metal wires and insulating materials such asSiO₂, a less distorted image can be produced than when it is irradiatedwith an electron beam having lower energy.

When damages must be taken into consideration, the breakdown may beincreased for gate oxide films and insulating thin films. In such acase, less distorted accurate images can be produced with less damagesby selecting an appropriate electromagnetic wave for irradiation. By theirradiation of electromagnetic wave, photoelectrons are emitted from asurface of a sample. Because of low emission energy, the electrons canmore readily achieve a focusing condition by an electo-optical system.For example, in an imaging optical system, it is possible to achieve aresolution of 0.1 μm or less, and a maximum image height of 50 μm ormore in the field of view.

As to an imaging optical system, it is composed such that electron beamsare irradiated on a field of view or evaluation range of a samplesurface to obtain an image of the field of view, enlarging the image byan electro-optical system, and inspecting the sample on the basis of theenlarged image. Namely, a system in which electron beams are irradiatedon a field of view extending at least one dimension on a sample (but notonly one point) to obtain an image, is generally called a system of “animaging type”.

As described above, the present invention permits a selection from thefollowing three approaches:

-   -   (1) Photoelectrons emitted from a sample surface irradiated with        an electromagnetic wave such as ultraviolet ray are detected to        generate an electron image of the sample surface;    -   (2) Secondary electrons emitted from a sample surface irradiated        with an electron beam are detected to generate an electron image        of the sample surface; and    -   (4) Photoelectrons and secondary electrons emitted from a sample        surface irradiate with both an electromagnetic wave such as        ultraviolet ray and an electron beam to generate an electron        image of the sample surface.

An appropriate approach is selected for use from the foregoing threeapproaches on the basis of a charging characteristic and anti-damagecharacteristic associated with a material, structure and the like of aparticular sample. In this way, it is possible to efficiently acquire anelectron image of a sample surface with high quality while preventingdamages on the sample. For example, a semiconductor wafer can beeffectively evaluated for detecting defects.

For the electromagnetic wave generator, a lamp light source such asmercury lamp, a deuterium lamp, an excimer lamp, or a laser light sourcemay be used as an ultraviolet ray source. Fourth-order harmonic waves ofArF, KrF excimer laser, Nd:YAG laser may be used as a laser. Theultraviolet ray or laser is guided by a light guide or an optical fiber,such that it can be irradiated onto a surface of a sample placed in avacuum chamber. Optical lenses may be used to control an irradiatedregion and an optical density.

Also, a resist film may be coated on a sample surface for preventing thesurface from being charged. While the irradiation of an electromagneticwave does not cause large charging, the resist film may be coated togenerate high quality images which are less distorted when an image isdistorted even with slight charging, or when small distortions must becorrected for generating a precise image. A resist film may be coated ona sample which is irradiated with an electron beam, in which case a lessdistorted image can be generated.

With the realization of the foregoing features, it is possible toprovide electron emission characteristics more suitable for theproperties of particular circuits and layered structures and efficientlygenerate high quality images while preventing damages and distortedimages.

In the example mentioned above, ultraviolet rays, ultraviolet laser,X-rays, X-ray laser may be used as the electromagnetic waves.Alternatively, photoelectrons may be emitted using visible light or thelike which has a wavelength longer than ultraviolet rays and X-rays. Thelatter sources can be applied when a sample has a small work function,when multiple photons are absorbed, and the like.

It is also possible to employ an imaging optical system for detectingelectrons emitted from a sample surface in order to improve a throughputfor evaluating the sample surface. For example, a detector usingMCP/screen/relay lens/CCD structure can be used for acquiring images inmultiple portions in a step & repeat system. Alternatively, a detectorusing MCP/screen/relay lens/TDI structure can be used for sequentiallyacquiring images.

Since the use of such an imaging optical system allows simultaneousdetection of electrons which are two-dimensionally emitted from a samplesurface, a two-dimensional electron image can be rapidly acquired. Asample can be evaluated for detecting defects and the like at a highthroughput, by utilizing this feature and the aforementioned detector.

Since a sample can be inspected or evaluated at a high throughput in themiddle of and after completion of a process using the aforementionedsurface inspection apparatus, semiconductor devices can be necessarilymanufactured at a high throughput.

A semiconductor device manufacturing system can be built to have asurface inspection apparatus using an electromagnetic wave, or a surfaceinspection apparatus using both of an electromagnetic wave and anelectron beam, and a surface flattening mechanism. For example, thesemiconductor device manufacturing system can be formed to associativelyarrange a wafer carrying mechanism, a surface inspection mechanism, asurface flattening mechanism, and a sample drying mechanism in such amanner that a dried semiconductor wafer is introduced into the surfaceprocessing apparatus and removed therefrom in a dried state.

The system may be additionally provided with a resin film coatingmechanism, a pattern forming mechanism, a developing mechanism, and adefect repairing mechanism.

FIG. 16 explanatorily shows a third embodiment of the inspectionmechanism or apparatus 700. The inspection apparatus in FIG. 16comprises a stage 770 on which a sample S is carried; an ultraviolet raysource 30 for generating an electromagnetic wave; an imaging opticalsystem 40 having three enlarging lens systems 41-43; a detector 50 fordetecting photoelectrons; and an image formation/signal processing unit60. Each of the lens systems 41-43 comprises two or more lenses for ahigh resolution and a high zooming ratio.

The sample S is, for example, a wafer in which circuit patterns areformed on silicon substrates, in the middle of or after completion of asemiconductor device manufacturing process. While the semiconductordevice manufacturing process includes a variety of steps, theultraviolet ray source 30 irradiates ultraviolet rays to the surface ofthe wafer to emit photoelectrons from the surface of the sample S, whichare detected by the detector 50 through the imaging optical system 40.An electric signal or an optical signal output from the detector 50 isprocessed in the image formation/signal processing unit 60 forevaluating the presence or absence of debris, defective conduction,defective patterns, drops and the like, state determination,classification and the like in all steps which include those in thesemiconductor device manufacturing process.

FIG. 17 illustrates a fourth embodiment of the inspection mechanism orapparatus 700. The apparatus of the fourth embodiment correspond to thethird embodiment shown in FIG. 16, provided that each of the lenssystems 41-43 of the third embodiment is replaced with a single lens. InFIG. 17, an aperture plate 44 is disposed between the second lens 42 andthe third lens 43 of the imaging optical system 40. The aperture plate44 is utilized for noise cutting, transmittance control and aberrationamount control. Though not shown in FIG. 16, a similar aperture plate isalso provided in the third embodiment.

In the fourth embodiment, a sample S is a silicon wafer having a size of8-12 inches is carried on an X-Y-θ control stage 770. The wafer isformed with circuit patterns of LSI in the middle of manufacturing. Adetector 50 used herein can be composed of an electronic amplifier, anopto-electronic converter and a TDI.

An ultraviolet ray source 30 used herein is a mercury lamp whichirradiates ultraviolet rays into a vacuum chamber (not shown) by anappropriate light guide (not shown) onto the surface of the sample S. Anultraviolet irradiation region is adjusted by optical lenses or the like(not shown) such that the region has a diameter approximately in a rangeof 0.01 mm to 10 mm. Photoelectrons are generated from the surface ofthe wafer by the irradiation of ultraviolet rays. The photoelectrons areguided to the detector 50 by the imaging optical system 40. Since theimaging optical system 40 can provide a focus scaling ratio ofapproximately 50-500 by the three lenses 41-43, the detector 50two-dimensionally detects a pattern on the wafer, resulted from adifference in photoelectron generation characteristics (such as aworking function) on the wafer surface, and the image formation/signalprocessing unit 60 forms images and processes signals. Through thesignal processing, defects are detected and classified.

Using the detector 50 and stage 770 in synchronism, wafers can beevaluated in sequence. The TDI detector can also detect electron imagesin sequence while the stage 770 is moved in sequence. The use of thisstrategy can save a loss time involved in stop/move and loss time untila moving speed is stabilized, as compared with the step & repeat system,thereby efficiently performing evaluations such as detection of defects.

While the third and fourth embodiments have shown examples in which theelectromagnetic rays are used as ultraviolet rays, X-rays may beirradiated instead.

FIG. 18 illustrates a fifth embodiment of the inspection mechanism orapparatus 700. In the fifth embodiment, ultraviolet rays and electronbeam can be selectively irradiated to a sample surface. The inspectionapparatus illustrated in FIG. 16 additionally comprises an electron beamirradiation system including an electron source (electron gun) 31 inaddition to the ultraviolet irradiation system including the ultravioletray source 30 in the inspection apparatus 700 illustrated in FIG. 16. AnExB deflector (filter) 45 is also provided for deflecting a primaryelectron beam.

A sample S is a silicon wafer of 8-12 inches which is carried on anX-Y-Z-θ control stage 770. The wafer is formed with circuit patterns ofLSI in the middle of manufacturing. A detector 50 used herein can becomposed of an electronic amplifier, an opto-electronic converter and aTDI.

The ultraviolet ray source 30 used herein is an Nd:YAG laser based UVlaser source for generating fourth-order harmonics (251.5 nm). A UVlaser is introduced into a vacuum chamber (not shown) by an appropriatelight guide (not shown) for irradiation onto the wafer S within thechamber. An ultraviolet irradiation region is adjusted by optical lensesor the like (not shown) such that the region has a diameterapproximately in a range of 0.01 mm to 10 mm. Photoelectrons aregenerated from the surface of the wafer by the irradiation ofultraviolet rays. The photoelectrons are guided to the detector 50 bythe imaging optical system 40.

When the electron beam irradiation is used, electrons generated from theelectron source 31 are guided to the surface of the wafer S through aplurality of lenses, aligners and apertures (none of them is shown), andthe ExB deflector 45 for deflecting the direction of an electron beam.The electron beam source 31 used herein can be an electron gun whichcomprises, for example, an LaB₆ cathode, a Wehnelt and an anode. Aprimary electro-optical system can be comprised of an aperture, analigner, an aperture, a quadruple lens for forming an irradiation beam,an aligner, the ExB deflector and the like. The electron beam thusintroduced can be controlled by the primary electro-optical system tohave a field of view, the diameter of which is approximately in a rangeof 10 μm to 1 mm. The irradiation field of view can be formed at anaspect ratio not equal to one, for example, ¼ (=x/y). The energy of theelectron beam irradiated to a sample can be selected from a range ofapproximately 0 to 4 kV.

In the fifth embodiment, the imaging optical system 40 can implement afocus scaling ratio approximately in a range of 50 to 500 by the threelens systems (a total of six lenses). In this event, electrostaticlenses used herein can satisfy the Wien condition in which electronsemitted from the wafer surface travel straight, while an irradiatedelectron beam is deflected toward the surface.

The detector 50 acquires through the imaging optical system 40 a patternproduced from a difference in the photoelectron generationcharacteristics (working function and the like) through the irradiationof ultraviolet rays onto the surface of the wafer S, or secondaryelectrons emitted from the surface of the wafer S irradiated by anelectron beam. The electrons from the surface of the wafer S aretwo-dimensionally detected by the detector 50, and applied to the imageformation/signal processing unit 60 for image formation and signalprocessing. Through the signal processing, the wafer S is evaluated fordetecting defects, classifying the defects, and the like.

Likewise, in the fifth embodiment, the surface of the wafer S can beinspected or evaluated sequentially by operating the detector 50 andstage 770 in synchronization. The TDI detector can also detect electronimages in sequence while the stage 770 is moved in sequence. The use ofthis strategy can save a loss time involved in stop/move and loss timeuntil a moving speed is stabilized, as compared with the step & repeatsystem, thereby efficiently performing evaluations such as detection ofdefects.

When the inspection mechanism 700 comprises an ultraviolet (orultraviolet laser) irradiation device and an electron beam irradiationdevice as in the fifth embodiment, either of the irradiation devices isselected for use with a particular wafer sample, depending ondifferences in material and structure. For example, when a semiconductorwafer has a structure near the surface which is susceptible tobreakdown, such as a gate oxide film, the ultraviolet rays (laser)should be irradiated to the wafer for evaluation. On the other hand, inan evaluation of a wafer Which is flattened after a wiring material hasbeen embedded, when a gate oxide film or the like is away from thesurface to an extent enough to be free from damages, an electron beammay be irradiated to acquire a high contrast electron image forevaluating the wafer. In this event, incident energy to the wafer ispreferably in a range of 2 to 3 keV.

For materials other than a semiconductor wafer, for example, livingsamples, polymer materials and the like, ultraviolet ray (laser)irradiation mechanism should be used if an irradiated electron beamwould cause charging so strong that the sample could be broken.

Both of the ultraviolet rays and electron beam can be irradiated to asingle sample. This method can minimize a potential difference betweenmetal and insulating materials both which are on a sample, to reducedistortions in image. Further, irradiating both the ultraviolet rays andelectron beam is also preferable when a larger amount of electrons isdesirably acquired from the surface of the sample.

In this event, the sample may be coated with a resist film. When thesample is irradiated with a highly intense electron beam and ultravioletrays (laser), the resist film coated on the sample can effectivelyprevent charging, thereby providing a high quality electron image withless distortions.

X-rays or an X-ray laser may be used instead of the ultraviolet rays orultraviolet laser as well in the fifth embodiment.

FIG. 19 illustrates a sixth embodiment of the inspection mechanism orapparatus 700. In the sixth embodiment, both of ultraviolet rayirradiation and electron beam irradiation are employed. An excimer lampis used for the ultraviolet ray source 30, and ultraviolet rays from thelamp is irradiated to a surface of a sample S through an appropriateoptical system (optical lenses and optical fiber). Electrons emittedfrom the sample S are guided to the detector through an imagingprojection type lens system.

An electron beam emitted from the electron beam source 31 having anelectron gun is reshaped by a square aperture, reduced in size by twolenses 33, 34, and focused at the center of a deflection plane of theExB deflector 45 in the shape of a square, one side of which is 1.25 mm,for instance. The electron beam deflected by the ExB deflector 45 isreduced to ⅕ by lenses 8, 9 (lens system 41) and irradiated onto asample S.

Electrons (including photoelectrons and secondary electrons) havinginformation of a pattern image, emitted from the sample S, are enlargedby four electrostatic lenses 9, 8, 12, 13 (corresponding to lens systems41, 42), and detected by the detector 50. The lenses 9, 8 make up asymmetric doublet lens, while the lenses 12, 13 also make up a symmetricdoublet lens, thereby providing distortionless lenses. However, sinceslight distortions may occur due to stains on the electrodes of thelenses, it is preferable that a sample having a standard pattern is usedto measure distortions and a parameter is calculated for correcting thedistortions.

When the sample S is a wafer Which is selectively formed with an oxidefilm and a nitride film, a correction for distortions in the opticalsystem is not sufficient. Therefore, when the detector 50 acquire imagedata, a representative point should be selected from a pattern edge forcomparison with the image data for correcting distortions. Then, defectsshould be detected through a die-by-die comparison or an image-by-imagecomparison.

In FIG. 19, a control electrode 15 is applied with an appropriatelyselected voltage to control the field strength on the surface of thesample S, thereby reducing aberration of electrons (secondary electronsand the like) emitted from the surface of the sample S.

FIG. 20 illustrates a seventh embodiment of the inspection mechanism orapparatus 700. In the sixth embodiment, an image detecting system basedon laser scanning is employed. The ultraviolet ray source 30 used hereingenerates a double wave (350-600 nm) or a triple wave (233-400 nm) of aTi:Al₂O₃ laser. Generated laser light is guided into a vacuum chamber(not shown) through an optical lens system 35, and is two-dimensionallyscanned by a mirror 36 such as a polygon mirror. With the use of thedouble wave or triple wave of the Ti:Al₂O₃ laser, a wavelength can bearbitrarily selected in a range of 233 to 600 nm. It is thereforepossible to select a wavelength which presents a high photoelectronacquisition efficiency for irradiation in accordance with the materialand structure of a sample. Photoelectrons are generated from portionsirradiated with the ultraviolet ray laser and detected by a detector 50which in turn generates an electric signal or an optical signal.

In this event, an image can be generated from the electrons emitted fromthe sample S in the following two modes:

1) Mode Based on Laser Scan and Imaging Optical System:

Photoelectrons emitted from the surface of the sample S through scanningof the laser light are focused on the detector 50 through the imagingoptical system. In this event, the photoelectrons focused on thedetector 50 are enlarged by a factor of 50-500 by the imaging opticalsystem while maintaining the coordinates of positions at which thephotoelectrons have been two-dimensionally emitted. The detector 50 canbe comprised, by way of example, of MCP/FOP/TDI configuration,MCP/fluorescent plate/relay lenses/TDI configuration, EB-TDIconfiguration, and the like. Also, a CCD may be substituted for the TDI.When the TDI is used, electron images can be acquired while the sample Sis moved in sequence by the stage 770. When the CCD is used, electronimages are acquired on a step & repeat basis because the CCD acquiresstill images.

Defects are detected in the images thus acquired in a die-by-die (orchip-by-chip) comparison or a image data based comparison.

2) Mode Based on Laser Scan and Second Detector:

A second detector 51 is an electron detector including a scintillator ora photo-multiplier, which comprises an electrode 52 for attractingphotoelectrons. This electrode 52 permits scanning of laser light to besynchronized with an electronic signal, so that a signal from the seconddetector 51 can be processed into an electron image. Defects on thesample is detected on the electron images produced from secondaryelectrons acquired by the second detector 51 by the imageformation/signal processing unit 60 through a die-by-die comparison or aimage data based comparison.

Next, explanation will be made on a method of manufacturingsemiconductor devices which includes procedures for inspectingsemiconductor wafers in the middle of a manufacturing process or afterthe process, using such a surface inspection system as shown in FIG. 9or such an inspection apparatus as shown in any of FIGS. 14-20. Asillustrated in FIG. 21, the method of manufacturing semiconductordevices, when generally divided, comprises the following steps:

-   -   1. A wafer manufacturing step S1 for manufacturing wafers        (alternatively, a wafer preparing step);    -   2. A wafer processing step S2 for processing wafers as required;    -   3. A mask manufacturing step S3 for manufacturing photo masks or        reticle masks required for exposure;    -   4. A chip assembly step S4 for dicing chips formed on a wafer        one by one and bringing each chip into an operable state; and    -   5. A chip testing step S5 for testing finished chips.

Each of the steps S1-S5 may include several sub-steps.

In the respective steps, a step which exerts a critical influence to themanufacturing of semiconductor devices is the wafer processing step S2.This is because designed circuit patterns are formed on a wafer, and amultiplicity of chips which operate as a memory and MPU are formed inthis step.

It is therefore important to evaluate a processed state of a waferexecuted in sub-steps of the wafer processing steps which influences themanufacturing of semiconductor devices. Such sub-steps will be describedbelow.

First, a dielectric thin film serving as an insulating layer is formed,and a metal thin film is formed for forming wires and electrodes. Thethin films are formed by CVD, sputtering or the like. Next, the formeddielectric thin film and metal thin film, and a wafer substrate areoxidized, and a mask (photo mask) or a reticle mask created in the maskmanufacturing step S503 is used to form a resist pattern in alithography step. Then, the substrate is processed in accordance withthe resist pattern by a dry etching technique or the like, followed byinjection of ions and impurities. Subsequently, a resist layer isstripped off, and the wafer is tested.

The wafer processing step S3 is repeated the number of times equal tothe number of required layers to form a wafer before it is separatedinto chips in the chip assembly step S4.

FIG. 22 is a flow chart illustrating the lithography step which is asub-step of the wafer processing step S2 in FIG. 21. As illustrated inFIG. 22, the lithography step includes a resist coating step S21, anexposure step S22, a development step S23, and an annealing step S24.

After a resist is coated on a wafer formed with circuit patterns usingCVD or sputtering in the resist coating step S21, the coated resist isexposed in the exposure step S22. Then, in the development step S23, theexposed resist is developed to create a resist pattern. In the annealingstep S24, the developed resist pattern is annealed for stabilization.These steps S21 through S24 are repeated the number of times equal tothe number of required layers.

In the process of manufacturing semiconductor devices, a test isconducted for defects and the like after the processing step whichrequires the test. However, the electron beam based defect testingapparatus is generally expensive and is low in throughput as comparedwith other processing apparatuses, so that the defect testing apparatusis preferably used after a critical step which is considered to mostrequire the test (for example, etching, deposition (including copperplating), CMP (chemical mechanical polishing), planarization, and thelike).

In the above-mentioned semiconductor device manufacturing method, adefect in flattening of a sample can be immediately detected anddetermined, thus enabling efficient process control. The surfaceinspection apparatus is capable of detecting not only a defect inflattening, but also a failure or a defect in a process prior toflattening. Therefore, process control can be conducted with respect toflattening and other processes conducted prior to flattening. Based oninformation obtained by this process control, it is possible toefficiently detect, rectify and improve a defect in each process whichhas been carried out. Further, an entire structure of an inspectionapparatus capable of conducting a series of operations betweenflattening and inspection can be simplified, and samples can be smoothlyconveyed using the system illustrated in FIG. 9, thus ensuring a highthroughput.

In summary, the present invention is advantageous in the followingpoints.

-   (1) According to the present invention, a defect in a wafer surface    can be correctly measured by suppressing distortion of a measurement    image due to electrification. Therefore, it is possible to conduct a    scanning operation using a high current, while the electric charge    on the wafer can be appropriately controlled, and a large number of    secondary electrons can be detected. Therefore, a detection signal    having a desirably high S/N ratio can be obtained, thus enabling a    defect to be detected with high reliability.-   (2) A high S/N ratio can be obtained, and image data can be produced    even when scanning is conducted at a high speed. Therefore, a    throughput in an inspection apparatus can be increased.-   (3) When an electron beam or an ion beam is emitted to a wafer, in    the case where the beam has energy as high as about 2 keV or more,    there is a possibility of a substrate or device circuits formed    thereon being damaged. This possibility can be reduced by effecting    observation or inspection according to the present invention. While    high beam energy causes device damage in conventional techniques,    such damage does not occur in the present invention and an electron    image having minimum distortion can be obtained.-   (4) A defect in flattening of a wafer can be immediately detected    and determined, thus enabling efficient process control. The surface    inspection apparatus of the present invention is capable of    detecting not only a defect in flattening, but also a failure or a    defect in a process prior to flattening. Therefore, process control    can be conducted with respect to flattening and other processes    conducted prior to flattening. Based on information obtained by this    process control, it is possible to efficiently detect, rectify and    improve a defect in each process which has been carried out.    Further, a yield of a device manufacturing process can be increased,    and a cost of manufacture of devices can be reduced.-   (5) In order to provide the above advantage, it is possible to use    an image processing system capable of determining the types of    defects generated in wafer surfaces. This image processing system is    capable of determining, for example, deposition of a foreign matter,    contact failure in circuits, and a defect in a pattern form.    Therefore, it is possible to determine, from an acquired electron    image, in which manufacturing process or which place in an apparatus    a defect was generated. Thus, a cause of a defect can be efficiently    improved and rectified.-   (6) According to the present invention, it has become possible to    manufacture devices by a method in which a defect in a wafer during    a process is detected by using the above-mentioned inspection    apparatus and method.-   (7) Loading/unloading robots, such as those used in a conventional    independent apparatuses, can be eliminated, thus simplifying an    entire structure of the apparatus and reducing a size of the    apparatus. Further, a process for conveyance of a wafer can be    simplified, thus increasing a throughput.-   (8) The respective mechanisms of the inspection apparatus are    disposed on a single base. Therefore, it is easy to conduct    adjustment of a work position of a wafer and a loading/unloading    position, which is difficult in a conventional system in which a    plurality of independent apparatuses are placed.-   (9) The number of utilities and control valves for supplying    compressed air, electricity, cooling water, pure water or ultrapure    water, a nitrogen gas, etc, can be reduced. Therefore, the    inspection apparatus can be simplified.-   (10) The possibility of exposing a wafer to an external environment    can be reduced, thus preventing contamination of wafers.

Although the present invention has been described above in detail withreference to the drawings, the foregoing description is for explanatorypurposes and not intended to limit characteristics. It should beunderstood that the foregoing description merely illustrates andexplains preferred embodiments, and all modifications and changes withinthe scope of the spirit of the present invention are protected.

We claim:
 1. A mechanism for inspecting a surface of a sample,comprising: an electro-optical inspection apparatus comprising: anelectromagnetic wave source for irradiating the sample surface withelectromagnetic waves; an electron source consisting of an electron gunfor emitting an electron beam in a direction which is not perpendicularto the sample surface; and an EXB deflector for deflecting the electronbeam emitted from the electron source to irradiate the sample surfacetherewith in a direction which is perpendicular to the sample surface,and passing photoelectrons emitted from the sample surface when it isirradiated with the electromagnetic waves, and electrons from the samplesurface when it is irradiated with the electron beam; a detector fordetecting the photoelectrons and electrons, respectively which arepassed through the EXB deflector to output electric signals associatedwith the detected photoelectrons and electrons, respectively; and aprocessing unit for processing the signals output from the detector andforming an image associated with the sample surface.
 2. A mechanismaccording to claim 1, wherein the electro-optical inspection apparatusfurther comprises an objective lens system comprising at least twolenses located between the sample surface and the EXB deflector, and anenlarging lens system comprising at least two lenses and located betweenthe EXB deflector and the detector.
 3. A mechanism according to claim 1,wherein the electro-optical inspection apparatus further comprises anobjective lens system comprising at least two lenses located between thesample surface and the FXB deflector, and two enlarging lens systemseach comprising at least two lenses and located between the EXBdeflector and the detector.
 4. A mechanism according to claim 1, whereinthe electro-optical inspection apparatus is an image projection typeinspection apparatus.
 5. A mechanism according to claim 1, wherein adiameter of the electromagnetic waves irradiated on the sample surfaceis in a range of about 10 μm-10 mm.
 6. A mechanism according to claim 1,a diameter of a field of view of the electron beam is about 10 μm-10 mm.7. A mechanism according to claim 1, further comprising a controlelectrode to supply a voltage to control a field strength on the samplesurface, to thereby reduce aberration of the photoelectrons or electronsemitted from the sample surface.
 8. A mechanism according to claim 1,wherein the sample is at least one of a semiconductor wafer with aresistive film thereon, a photo-mask and reticle-mask.
 9. A mechanismaccording to claim 1, wherein the electromagnetic wave source irradiatesthe sample surface with the electromagnetic waves in a direction whichis not perpendicular to the sample surface.
 10. A method of inspecting asurface of a sample, comprising: actuating one or both of theelectromagnetic wave source and the electron source in accordance with akind of the sample; irradiating the sample surface with one or both ofthe electromagnetic waves and the electron beam which are/is emittedfrom the actuated source; detecting either of photoelectrons andelectrons emitted from the sample surface by the detector to output thesignal; and processing the signal by the processing unit to obtain animage of the sample surface.
 11. A method according to claim 10, whereinthe sample surface is coated with a resistive film.